Author Topic: Con Rod Bearing?  (Read 3715 times)

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Offline mqtsteve

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Con Rod Bearing?
« on: March 02, 2014, 08:01:29 AM »
I'm rebuilding two BS90's.  Would like to change the connecting rod bearings(big end).  What do I need to do?  Send them to a specialist?  If so, who?  Any help would be appreciated.
« Last Edit: March 02, 2014, 10:07:16 AM by mqtsteve »
Steve S.
4/1966 BS90 Sport(o.i.), 5/1966 BS90 Sport(o.i.),
1965 BS90 Trail, 1965 BS90 Mountain

Online dcr

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Re: Con Rod Bearing?
« Reply #1 on: March 02, 2014, 11:21:18 AM »
Somehow I read crank bearing but was thinking upper rod bearing. Not sure how that all came out, but the multi-piece cranks need pressed apart as well as pressed back together. Apart isn't overly difficult as you are simply using a hydraulic press to press out the pin. Quite simple for a single cylinder but a lot more complex for the twin cylinder crank. 

Back together requires some specialized stuff. Crank builders have a jig or boxframe which aligns the pieces of the crank to ensure symmetry and alignment.

My apologies to the machinists out there that I offended with my "hammer and punch" reply. I blame global warming, shrinking polar ice caps and acid rain.
« Last Edit: October 02, 2014, 10:41:00 AM by dcr »
1966 175 DT and 1968 350 GTR

Offline mqtsteve

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Re: Con Rod Bearing?
« Reply #2 on: March 02, 2014, 12:24:52 PM »
Thanks dcr!  No precise measurements needed?  Are the connecting rod, crank pin and piston pins reusable?
Steve S.
4/1966 BS90 Sport(o.i.), 5/1966 BS90 Sport(o.i.),
1965 BS90 Trail, 1965 BS90 Mountain

Offline bsracer

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Re: Con Rod Bearing?
« Reply #3 on: March 02, 2014, 01:16:13 PM »
Changing the Big end bearing requires a little bit of some expertise. A shop press is needed. The pin ( if the bearing is bad so is the pin) is usually replaced along with the bearing and shims. The webs or crank halves need to be positioned correctly and pressed together. They can easily get out of position and sometimes need a wedge to space them properly. The shims can easily be pinched. The webs can be slightly turned from correct position. Truing is an art form in itself. You may want to Google to see if there are videos on how to do it. You can always send it off to someone who has the know how to do it. Even tapping a crank out of the cases can "knock the crank out of true".


paul


Offline william anderson

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Re: Con Rod Bearing?
« Reply #4 on: March 02, 2014, 04:10:34 PM »
 thanks ,  bsracer  for adding your words of wisdom , when first reading that lower end crank pin could be removed with a punch an hammer , cold shivers ran down my back as a experinced motorcycle tech, i would never suggest that method , i have spent pains taking cranks apart an pressing together,  you need a good press,  a crank jigg or at least metal plates to support the crank halves , a good staight edge , feeler gages , v-blocks for truing , a set of mic. , brass hamer , an yes there is thrust washer side clearance on cranks , very important  , thanks william anderson :o
william anderson

Offline mqtsteve

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Re: Con Rod Bearing?
« Reply #5 on: March 02, 2014, 05:37:04 PM »
Thanks guys!!  I thought it was more involved.  Is there any crank builders you could recommend?
Steve S.
4/1966 BS90 Sport(o.i.), 5/1966 BS90 Sport(o.i.),
1965 BS90 Trail, 1965 BS90 Mountain

Offline william anderson

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Re: Con Rod Bearing?
« Reply #6 on: March 02, 2014, 06:19:46 PM »
hi mgtsteve ,  i now longer have time with my current job taking up all my time but you may want to contact   steve reed here on the bridgestone site , steve is a reliabe tech an very capable of completing the job , thanks william anderson
william anderson

Online dcr

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Re: Con Rod Bearing?
« Reply #7 on: March 02, 2014, 09:05:41 PM »
Everyone has a preference. Done it too many times to count and never had an issue.

Here is a pic of me at a motorcycle master mechanics training session.
1966 175 DT and 1968 350 GTR

 


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